1993: 5 of a total of 7 (72%) patients achieved total eradication of their cancer (R/R AML), page-21

A few comments on this comparison @wombat777

1. The PTX200 trial was a Phase I dose escalation trial for safety, not a Phase II trial. Phase I safety trials are not intended to determine if your drug works, but what is the maximum tolerated dose (MTD). Most of the patients in the trial will get a sub-optimal dose of the drug because you start these MTD trials with a low dose and increase. It is not really appropriate to compare the efficacy results of a Phase I trial with Phase II trials.

2. In oncology you almost always treat 18 patients (3+3 protocol) in a dose escalation Phase I study unless your trial is stopped early for safety.The regulatory authorities (FDA) are most concerned about safety and it is not a good sign for the prospects of your drug to have the Phase I trial stopped early for safety concerns. At the very least if you are allowed to continue you are going to have to go back and do another safety study before progressing.

3. The PTX-200 trial was not a single agent trial as the patients were treated with both PTX-200 & cytarabine [1]. While cytarabine is part of the standard induction treatment that all fit AML patients get (it is the 7 of the "7+3” chemo), it also works as a salvage treatment on its own in a reasonable percentage of relapsed AML patients. It is standardly used as a treatment in relapse AML and some of the historical trials showed that more than 50% of relapse patients go into CR after being given cytarabine on its own [2]. While we would all like to know how well PTX-200 works, we can’t at this stage know the reason the 3 patients went into CR in the trial. While I hope it was because of PTX-200 (we still need many more new drugs for treating AML), we don’t really know.

4. One of the huge advantages we have with Bisantrene is the historical trials were done before combination trials became basically compulsory. From a scientific point of view it would have been much better for PTX to have run the PTX-200 trial as a single agent trial, but the FDA won’t allow you to run such a trial these days. We know that Bisantrene works since it was the only drug used in the old trials, while these days companies with new drugs have a much harder time showing their drug works.

1. https://en.wikipedia.org/wiki/Cytarabine
2. https://ascopubs.org/doi/abs/10.1200/JCO.1985.3.7.992